Solar cells and solar modules convert sunlight into electricity. These electronic devices have been traditionally fabricated using silicon (Si) as a light-absorbing, semiconducting material in a relatively expensive production process. To make solar cells more economically viable, solar cell device architectures have been developed that can inexpensively make use of thin-film, light-absorbing semiconductor materials such as copper-indium-gallium-di-(sulfo-selenide, Cu(In, Ga)(S, Se)2, also termed CI(G)S(S). This class of solar cells typically has a p-type absorber layer sandwiched between a back electrode layer and an n-type junction partner layer. The back electrode layer is often Mo, while the junction partner is often CdS. A transparent conductive oxide (TCO) such as zinc oxide (ZnOx) typically doped with aluminum is formed on the junction partner layer and is typically used as a transparent electrode. CIS-based solar cells have been demonstrated to have power conversion efficiencies exceeding 19%.
High throughput production methods are in development to manufacture this type of thin-film photovoltaic device. As improvements are made for high throughput production of the absorber layer in such thin-film devices, similar advances need to be made with regards the deposition or formation of the junction partner layer to prevent bottlenecking of the production process.
It should be understood, however, that the materials used for forming the junction partner can contain toxic material and difficulties are encountered in improving the manufacturing system. One process for forming the junction partner involves using Group II-VI compounds such as CdS. The CdS used in the formation process may create hazardous waste by-products, thus increasing processing costs. Known processes are also inefficient or unreliable in creating a system with high throughput and high yield. Some known systems either use too much starting material, much of which is wasted during production. Others use systems that may be susceptible to imperfections in the underlying substrate that may cause non-uniform deposition of the junction partner material over a wide web. Therefore, a need exists in the art for an improved junction partner deposition system.